The Skull as a Whole. 137 



A considerable portion of the anterior and dorsal wall of the 

 orbit is formed by the facial complex. Dorsally, the roofing 

 element of this region, the frontal bone, bears a curved lateral 

 projection, the supraorbital process (processus supraorbital), 

 which overhangs the orbit. Its narrower base expands into anterior 

 and posterior tips, which lie parallel to the adjacent portion of the 

 skull, and enclose with the latter corresponding anterior and 

 posterior supraorbital incisures. The latter are converted 

 by ligament into foramina. The anterior wall of the orbit is formed 

 in part by a loosely articulated element, the lacrimal bone, the 

 lateral margin of which projects from the orbital rim as a blunt 

 subcutaneous process (processus subcutaneus). On the ventral 

 side of its base is the orbital opening of the nasolacrimal canal 

 (canalis nasolacrimal), the bony enclosure of the nasolacrimal 

 duct, which in the natural condition leads from the corneal surface 

 of the eye to the anterior portion of the nasal fossa. A smaller 

 projection forming the ventral boundary of the nasolacrimal 

 aperture is the hamulus lacrimalis. Finally, in the ventral 

 anterior angle of the orbit, the bases of the three posterior cheek- 

 teeth encroach to a considerable extent on the orbital space. They 

 are separated from the orbital wall by a deep infraorbital groove 

 (sulcus infraorbitalis), which leads forward into the canal of the 

 same name. They partly conceal two important apertures of this 

 region, the orbital opening of the pterygopalatine canal (canalis 

 pterygopalatine), leading to the palatal surface, and the spheno- 

 palatine foramen (foramen sphenopalatinum), leading to the 

 nasal fossa. The pterygopalatine canal opens ventrally in the 

 palato-maxillary suture of the hard palate by a rounded aperture, 

 the greater palatine foramen (foramen palatinum majus). 



The nasal cavity (cavum nasi) is enclosed by the maxilla and 

 premaxilla, with the assistance of paired roofing elements, the 

 nasal bones. Apart from the incisive foramina, which are closed 

 in the natural condition, the cavity is open at two points. Poste- 

 riorly it communicates with the ventral surface of the skull by the 

 choanae, which, in the rabbit, are incompletely divided. An- 

 teriorly it opens to the outside by the piriform aperture (apertura 

 piriformis). The cavity is divided into right and left portions, 

 the nasal fossae. In the divided skull it is seen thar the division 

 is effected chiefly through a median vertical, cartilaginous plate, 



